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Formulation of Petroleum and Alternative – Jet Fuel Surrogates
Peter S. Veloo Exponent, Failure Analysis Associates, Los Angeles, CA
Sang Hee Won & Frederik L. Dryer Department of Mechanical and Aerospace Engineering, Princeton University, NJ
Stephen Dooley Department of Chemical and Environmental Sciences, University of Limerick, Ireland
The 7th International Aircraft Fire and Cabin Safety Research ConferencePhiladelphia, PA
5th December 2013
2
Gas Turbines and Chemical Kinetics
Coupling chemical kinetics and computational fluid mechanics for engine design
Kinetically limited processes Nitrogen oxide production Soot formation Flame stability Blow out
J Campbell, J. Chambers, Patterns in the sky: natural visualization of aircraft flow fields. NASA SP-514,1994
3
Aviation Fuels – Composition
Distillation Temperature
Carbon Number Distributions Hydrocarbon Class Distribution
T. Edwards, L.Q. Maurice, J. Propulsion Power 17 (2001)
JP-4
JP-8
JP-7
Cycloparafinsn-Parafins
Naphthalenes
i-Parafins
Alkylbenzenes
4
Aviation Fuels – Fuel Variability
12 14 16 18 20 22 240
5
10
15
20
25
30
35
40
Volume %
Perc
enta
ge o
f Tot
al V
olum
e
Aromatics Content
36 39 42 45 48 510
10
20
30
40
50
Cetane Index
Perc
enta
ge o
f Tot
al V
olum
e
Cetane Index
Significant variability in physical and chemical properties
Current certification not highly constraining
Petroleum Quality Information System Annual Report (2009)
Fraction of delivered JP-8 fuels with specified properties
5
Surrogate Fuel Concept
Computational fluid dynamics coupled with detailed chemical kinetics requires a simplified fuel model
Am
ount
Molecular Weight
Surrogate Diesel
Am
ount
Molecular Weight
Real DieselReal Fuel
Surrogate FuelAbun
danc
eDistillation Temperature
Ideal surrogate fuel must emulate combustion behavior and physical properties of a target real fuel
6
Surrogate Fuels – Previous Work
Numerous jet fuel surrogate postulations present in literature (e.g.): Sarofim et al. ─ Surrogate fuel to model jet fuel pool fires Bruno et al. ─ Surrogate fuel to model thermo-physical
properties of jet fuel
Require detailed characterizations of target fuel (GC, NMR, …)
Significant uncertainty in chemical kinetics of selected surrogate compounds
Sarofim et al., Combust. Sci. Tech, 177 (2005) 715–739 T.J. Bruno et al., Ind. Eng. Chem. Res 45 (2006) 4371–4380
7
Surrogate Fuels – Present Approach
GOAL: Emulate gas phase combustion behavior of a target jet fuel
C4
C3
C2
C1
CH3O C2H5 C2H3 CH3O2
CH3 HCO HO2
H O OH
Real fuels – Many generic initial chemical functionalities
Fewer distinct chemical functionalities after initial oxidation
Distinct functionalities govern radical and small species
concentrations
Surrogate fuel need only reproduce:
distinct chemical functionalities
9
Surrogate Fuels – Present Approach
GOAL: Emulate gas phase combustion behavior of a target jet fuel
Identified critical combustion property targets: Adiabatic flame temperature Enthalpy of combustion Flame speed / burning rate Fuel diffusive properties Sooting propensity Auto-ignition
• Manifest in important practical combustion behavior
• Surrogate fuel must emulate critical fuel properties of target real fuel
10
Surrogate Fuels – Present Approach
Quantify critical fuel property targets: Adiabatic flame temperature
Enthalpy of combustion
Flame speed / burning rate
Fuel diffusive properties
Sooting propensity
Auto-ignition
The ratio of hydrogen to carbon (H/C)-CHN analysis (ASTM D5291)
Smoke point measurement (ASTM D1322)
Average molecular weight (MWavg)
Derived cetane number (ASTM D6890)
11
Case Study 1 – Fuel Surrogate for Jet A
n-Alkanes28%cyclo-Alkanes
20%
iso-Alkanes29%
Alkylbenzenes18%
Naphthlenes2%
Selected Surrogate Fuel Components
n-Dodecane
iso-Octane
n-Propylbenzene
1,3,5-TrimethylbenzeneDooley et al., Combust Flame (2010) 157:2333-2339Dooley et al., Combust Flame (2012) 159: 1444-4466
12
Surrogate Fuel Formulation Algorithm
Characterize target Jet A
Characterize surrogate components and their
mixtures
Emulate H/C, DCN, TSI, MWavg
Compare gas phase combustion characteristics
between surrogate and target
Experimental observations• Intermediate species profiles • Flame speeds / extinction limits• Soot volume fraction• Ignition delay times
Regression analysis to determine surrogate composition
Characterize target Jet A• H/C • Cetane number• Smoke point• Average molecular weight
Develop library of target measurements for individual and mixtures of surrogate components
13
Surrogate Fuel Compared with Real Jet-A Fuel
Equivalence Ratio, f0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
35
40
45
50
55
60
65
70
- Jet A - SurrogateLa
min
ar F
lam
e Sp
eed,
cm
/s p = 1 atm, Tu =400 K
Laminar Flame Speeds
Dooley et al., Combust Flame (2010) 157:2333-2339Dooley et al., Combust Flame (2012) 159: 1444-4466
14
Surrogate Fuel Compared with Real Jet-A FuelEx
tincti
on S
trai
n Ra
te, s
-1
Fuel Mass Fraction, XY
- Jet A - Surrogate
Extinction Limits
Dooley et al., Combust Flame (2010) 157:2333-2339Dooley et al., Combust Flame (2012) 159: 1444-4466
15
Surrogate Fuel Compared with Real Jet-A Fuel
Soot Volume Fraction
- Jet A - Surrogate
Radial Location (mm)
Soot
Vol
ume
Frac
tion
(ppm
)
Dooley et al., Combust Flame (2010) 157:2333-2339Dooley et al., Combust Flame (2012) 159: 1444-4466
16
Case Study 2 – Fuel Surrogate for S-8
Mono-methylated Alkanes
61% Di-methylated Alkanes
25%
Normal-Alkanes12%
Selected Surrogate Fuel Components
n-Dodecane
iso-Octane
Dooley et al., Combust Flame (2012) 159: 3014-3020
17
Surrogate Fuel Compared with Real S-8
1000K/T
Igni
tion
Del
ay T
ime
Shock tube ignition delay times
Dooley et al., Combust Flame (2012) 159: 3014-3020
18
Chemical Kinetic Modeling
Large spread in predictions using latest chemical kinetic reaction models for surrogate components Lack of consensus within kinetic modeling community
19
Uncertainties in Numerical Calculations
Propagation of uncertainties from rate parameters to numerical simulations
Numerical Uncertainty
20
Concluding Remarks
Demonstrated surrogate fuel methodology to capture gas phase combustion behavior of aviation fuels
Reaction model rate parameter uncertainties require further reduction
Application of surrogate concept to polymer combustion Determine surrogates that represent functionalities present
in gas phase pyrolysis products